1. Field of the Invention
The present invention relates generally to safety and efficiency of train movement. More particularly, the present invention is in the field of railroad signaling and train control, including positive train control (PTC), centralized traffic control (CTC), automatic block signaling (ABS), and communications-based train control (CBTC).
2. Background of the Invention
Rail breaks, unintentionally misaligned turnouts, and occupied track present potential hazards to moving trains. Traditionally, rail breaks, misaligned turnouts and occupied track are directly detected by use of track circuits. Railroad track is physically divided into electrically distinct blocks. An electrical current is caused to flow from a source located at the terminus of each block, through the rails, and is detected at both ends of the block, forming a track circuit.
Electrical current in a track circuit is detected by an electronic circuit or by use of an electromechanical relay. The presence of current in a track circuit indicates electrical continuity in the rails and thus the absence of broken rail. The absence of current indicates that either a broken rail or open switch is causing an electrical open circuit, or that the presence of a train is shunting current between the rails, causing a short circuit. In either case, the current will not be detected. Either condition indicates a potential hazard, and will cause the wayside or in-cab signaling system governing movement on the track to indicate a “stop” condition. Information that the block, or one of a group of blocks, is unavailable or occupied may also be communicated to a central train dispatching system.
A fundamental limitation of such traditional fixed-block wayside signaling systems is that by dividing railroad track into discrete blocks, they impose a limit on how closely trains can approach each other and still sense both broken rail and occupied territory ahead; thus they artificially limit maximum traffic density and therefore fundamentally restrict how efficiently a given track can be utilized. It therefore would be highly desirable to have a true “moving-block” or “virtual block” signaling system, whereby moving locomotives would have the ability to detect rail breaks or occupied track ahead of (or behind) their current positions, rather than being dependent on traditional fixed-block track circuits for rail break, open switch, and track occupancy detection.
A second fundamental limitation of traditional fixed-block track circuit systems is their inherent inability to detect a rail break which occurs ahead of or behind a moving train within the same block as the train. Also undetectable with track circuits is a rail break between two trains in the same block. In a traditional fixed-block track circuit, the loss of current from one end of the block to the other, caused by (intended) track occupancy is indistinguishable from the loss of current caused by a broken rail. It would be highly desirable not to lose the ability to detect broken rail when a block is occupied.
A third fundamental limitation of traditional track circuits is that they require installation of considerable track infrastructure, such as insulated joints between blocks, bond wires to ensure continuity between rail sections, wayside power, and wayside relay-based, code-relay, or (more commonly) electronic systems. This infrastructure and equipment is costly to install and requires very significant ongoing maintenance. It would be highly desirable to reduce these costs and simplify the track structure.
A fourth fundamental limitation of traditional track circuits is that they are not usually optimized to detect rail breaks, but instead are optimized for wayside signal system operation. It would be desirable to have better wayside detection of broken rails to improve train safety.
The present invention overcomes these fundamental limitations by eliminating the need for traditional, fixed-block track circuits for rail break detection, open switch detection, and track occupancy. By using equipment affixed to the leading or trailing locomotive(s) or cars of a train, in conjunction with passive (or active) shunts installed in the railroad track bed, and eliminating expensive wayside track circuit apparatus and associated track components used in traditional track circuits, the present invention reduces considerably both the track infrastructure cost and ongoing maintenance costs needed to detect broken rail and track occupancy.
Further, the present invention can be implemented in such a way so as not to be incompatible with existing traditional track circuit-based block signaling systems; it will not interfere with track circuits and wayside signal systems, if encountered, thus serving as an additional broken rail detection system capable of working in tandem with, and further, allowing existing traditional fixed-block systems to be optimized for broken rail detection.
A limitation of some implementations of PTC or CBTC systems that employ GPS data to determine which track a train is travelling on in multiple track territory is that even the best available GPS systems are unable to reliably distinguish which of two adjacent tracks a train is occupying with sufficient accuracy to be considered certain for safety-critical applications. An embodiment of the present invention solves this problem by providing the PTC system with a continuous, positive, unambiguous indication of which track the train is travelling on. This is a great advantage for practical implementation of a PTC system.
When used in conjunction with a route database or GPS location data, the present invention is capable of providing an additional method of estimating of train position, which can be optimally combined with GPS or other location system data or can be supplied to the CBTC/PTC system. The present invention is also able to detect rail breaks and track occupancies for a distance ahead of (or behind, if the system is mounted on the rear of the train) a moving train, enabling an improved implementation of CBTC/PTC.